In order to reduce a cooling load and to enhance comfort, a heat-reflecting glass sheet is known that reflects infrared rays (i.e., heat-ray) in sunlight. A conventional heat-reflecting glass includes a metal film, a transparent conductive film, or a nitride film. As a film capable of enhancing reflection of infrared rays while keeping a high transmittance of visible light, a heat-reflecting film is known that includes a multi-layered structure of metal oxide/metal/metal oxide.
When an optical device is used in a vehicle provided with a glass sheet that has a heat-reflecting film including a metal film, light from the device is attenuated while passing through the heat-reflecting film. The optical device for a vehicle is, for example, a rain sensor that can optically detect adhering water droplets on the outer surface of a windshield. In the rain sensor, a light-emitting element provided on the inner surface of the windshield emits light, and light reflected from the outer surface of the windshield is received by a light-receiving element provided on the inner surface, whereby the presence/absence of droplets of water on the outer surface is detected based on the intensity of reflected light. In this case, light for detection passes through the heat-reflecting film at least twice. Thus, the sensitivity of detecting water droplets adhering to the surface of the windshield is degraded.
JP 8(1996)-210042 A discloses a window used with a transmitter and/or a receiver that function particularly in an infrared range, wherein an infrared-rays reflecting and/or absorbing layer is disposed on the entire surface of the window excluding a surface region for transmission of the infrared light for the transmitter and/or the receiver. However, JP 8(1996)-210042 A discloses a window used with a communication tool rather than a detecting device.